Adaptive acceleration knock control

ABSTRACT

For eliminating acceleration knocking in spark ignition engines, the ignition is retarded when the engine is in dynamic operation by an amount which is optimized for the ambient conditions present at the start of each dynamic operation. The occurrence of knocking of the engine during acceleration is detected, and the amount of change of an engine operation parameter for a next acceleration is adjusted depending on whether or not the knocking during acceleration is occurring.

BACKGROUND OF THE INVENTION

The present invention relates to engine knock control systems in whichan operating parameter such as the ignition timing is varied duringdynamic operation i.e. acceleration, to prevent acceleration knocking.

At high cooling water and/or intake temperatures, audible accelerationknocking can occur in internal combustion engines if the load isincreased very quickly, i.e. during dynamic engine operation. Knockingcan be eliminated by retarding engine ignition. Therefore it has beenproposed to temporarily retard engine ignition during dynamic engineoperation to prevent the occurrence of acceleration knocking. Inconventional knock-control systems if dynamic engine operation isdetected the ignition is retarded by a fixed amount. However, retardingignition has an adverse affect on engine response (gas emission) andtherefore it is desirable to retard ignition as little as possible. Theknown systems for preventing acceleration knocking retard the ignitioneach time dynamic engine operation occurs, regardless of the ambientconditions. Thus, there may be instances when the ignition is retardedunnecessarily or more than is necessary.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome this disadvantage andoptimize the amount by which the ignition is retarded during each engineoperation.

The present invention provides a method of mitigating accelerationknocking in internal combustion engines comprising the steps of sensingacceleration of the engine and changing a particular engine operatingparameter in response to the sensing of acceleration, characterized bythe steps of detecting the occurrence of knocking during accelerationand adjusting the amount of change of the parameter for the nextacceleration depending on whether or not acceleration knocking isoccurring.

Preferably the operating parameter is the ignition timing which isretarded in response to the sensing of acceleration.

Preferably the detecting step includes examining the intensity ofacceleration knocking and adjusting the amount of retardation or changeof some other operating parameter in dependence on the intensity. Theamount of change is preferably adjusted when the knock intensity isoutside a predetermined range. The knock intensity may be examined atregular intervals during a predetermined time after the sensing ofacceleration.

The method is applicable to diesel engines as well as spark ignitionengines. In diesel engines the injection timing is adjusted to mitigateknocking.

The method of the invention as applied to a spark ignition engineensures that during dynamic operation the ignition angle is retardedjust enough to avoid knocking combustion. The method is adaptive in thatthe amount of retardation is optimized for the ambient conditionspresent during each engine operation (for example intake airtemperature, cooling water temperature, fuel quality, deposits in thecombustion space etc.)

A particular advantage-is that a better engine response can be achieved,particularly during warm running and when using knock resistant fuel.

For example, if a driver changes from normal fuel to knock-resistantfuel, the retardation of the ignition necessary for each accelerationmay be significantly less. According to the invention, next time theengine is operated (i.e. the vehicle is driven) the amount ofretardation will be adjusted at every instance of acceleration until theamount of retardation during acceleration reaches an optimum value.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to (e) illustrate the method of the invention graphically and

FIG. 2 is a flow chart detailing the steps of the method.

DESCRIPTION OF A PREFERRED EMBODIMENT

The illustrated embodiment of the present invention is intended fortemporarily retarding ignition only during dynamic engine operation. Anormal knock control system of known type controls the ignition angle atother times. The method thus forms part of a larger engine knock controlsystem which would typically be implemented by a computer. The methodmay be carried out as a series of steps as illustrated in FIG. 2 of thedrawings and may be controlled by clock pulses from a microprocessor.

The steps shown in the flowchart of FIG. 2 can be grouped into threestages, indicated by routes I, II and III on the flowchart. During thefirst stage I it is established whether or not dynamic engine operationis taking place. If dynamic engine operation is taking place, theignition timing for the next following ignition cycles is retarded by anamount determined in a manner to be described below. Then the amount ofretardation will be decreased during a defined time depending on theamount of retardation. During the second stage II the intensity of anyknocking occurring is examined. During stage III the amount ofretardation is changed if necessary, for the next dynamic operation oracceleration, so as to bring the knock intensity closer to the knocklimit. Each of these three stages may be carried out for each cylinderof the engine. The individual steps in each of stages I, II and III willnow be described in further detail.

Dynamic engine operation occurs when the engine load increases veryquickly. In the embodiment of the invention described herein themanifold pressure is used as a measure of engine load. The manifoldpressure is measured at regular intervals, preferably at a certaincrankshaft angle with the working stroke of each cylinder. A sample andhold circuit may be used for this purpose. The interval Δ T is equal tothe interval between two dynamic engine operations. When the manifoldpressure or engine load is increasing, as indicated in the graph "L"shown in FIG. 1(a) the engine load is low pass filtered to produce thecurve LF also shown in FIG. 1(a). If the "steps" in the graph L are verysteep this indicates that the engine is in dynamic operation. The"steepness" of the steps is determined by calculating the differencebetween the engine load and the filtered engine load, i.e. thedifference between the graphs of L and LF.

Thus, at step 1 of the flow chart of FIG. 2 the question is askedwhether dynamic engine operation is occurring by examining the values ofL and LF. DYNERK is a set value of L-LF above which dynamic engineoperation is said to be occurring. If L-LF>DYNERK, step 2 is thencarried out.

At step 2 a timer/counter is set to an initial value DYNANZ andimmediately begins to run down from that value. At step 3 a valueLAST/ZW1 is fed into a random access memory (RAM) LAST ZW2. LAST ZW2stores values for the retardation of the ignition during dynamic engineoperation. Thus once dynamic engine operation has been established LASTZW1 is fed into LAST ZW2 and the ignition timing is retarded by theamount LAST ZW1. (It will be understood that during normal conditionsthe engine would operate using stored characteristic values of ignitionangle for certain conditions of speed and load.) At step 4 a flag is setto indicate that dynamic engine operation is occurring. The steps arefollowed through in sequence at each clock pulse. Steps forming theremainder of the knock control system are carried out after step 4 andthe system begins again at step 1 at the next clock pulse. Thiscompletes stage I of the operation.

If at the next clock pulse the equation L-LF >DYNERK is still satisfied,steps 2 to 4 are simply carried out again.

If L-LF<DYNERK, step 5 is carried out. Here, the value in the RAM LASTZW2 is decremented by a set amount ABREKO. This step is carried out ateach next clock pulse while L-LF<DYNERK, with the limitation that LASTZW2 is not reduced below zero. Thus, after an initial sharp increase inengine load the ignition is retarded by the amount LAST ZW1, and thenthe amount of retardation is gradually reduced to zero so that theignition angle returns to its normal (non-dynamic) value.

At step 6 the content of the timer/counter is examined. If the timedefined by DYNANZ has not expired the next step carried out is step 7,which begins stage II of the operation. Here the intensity of anyknocking which is occurring is examined. At step 7 a comparison is madebetween the measured knock intensity and a set value DYNKF. If the knockintensity is greater than DYNKF, an acceleration knocking flag is set to1 at step 8. If the knock intensity is less than DYNKF, the knockintensity is compared to a second set value NORMKF at step 9. NORMKFindicates that the engine is operating at the knock limit, as desired.Any knocking requiring corrective action will have an intensity greaterthan NORMKF. If the knock intensity is smaller than NORMKF thisindicates that the engine is operating below the knock limit. If theknock intensity is smaller than DYNKF but greater than NORMKF a normalknocking flag is set to 1 at step 10.

Thus, at each clock pulse during the time DYNANZ and once L-LF is nolonger greater than DYNERK, the intensity of knocking is examined.

Once the time DYNANZ has expired, the answer to the question at step 6will be yes and the next step carried out will be step 11, which beginsstage III of the operation. At step 11 the "Dynamic" flag is examined.If dynamic operation is not in progress the only further step is to setthe normal knocking flag to zero at step 12. If dynamic operation isoccurring then after the dynamic flag has been examined at step 11 it isset to zero at step 13.

At step 14 the acceleration knock flag is examined. If this flag has notbeen set the normal knock flag is examined at step 15. If the normalknock flag has been set it is simply set to zero at step 12. If thenormal knock flag is not set i.e. the knock intensity is below the knocklimit, the amount of retardation of the ignition defined by ZW1 isadjusted since the retardation adversely affects the gas emission. It isdesirable for the amount of retardation to be optimized so that it is assmall as possible whilst ensuring that knocking above the defined knocklimit does not occur. If the knock intensity is equal to or below NORMKFit may be possible to lessen the amount of retardation without knockingoccurring. Therefore, if the knock intensity is equal to or belowNORMKF, the value of ZW1 is decremented by δ ZW1 at step 16, subject tothe limitation to zero at step 17 to ensure that the ignition is notbrought forward from its normal characteristic angle ALFA₋₋ Z.

If it is found at step 14 that acceleration knocking of intensitygreater than DYNKF is occurring the amount of retardation of theignition ZW1 is adjusted. If knocking is occurring the ignition must beretarded more to prevent further knocking. Thus, at step 18 theacceleration flag is reset to zero and at step 19 the value of ZW1 isincreased by ΔZW1, subject to an upper limit at step 20.

At the next clock pulse if the answer at step 1 is NO, steps 5 and 6will be carried out but this time at step 7 the dynamic flag will be atzero and steps 13 to 20 will not be carried out.

At the next "step" on the graph illustrated in FIG. 1(a) whenL-LF>DYNERK again, i.e. at the next dynamic operation, or accelerationthe new value of ZW1 obtained at steps 13 to 20 will be set forretarding the ignition, and stages I, II and III will be repeated. If itis determined during stage II that the knock intensity is still greaterthan DYNKF or smaller than NORMKF using the new value of ZW1, ZW1 willbe increased or decreased during stage III.

Thus, ZW1 will be adjusted every time the condition L-LF>DYNERK issatisfied until the knock intensity is between NORMKF and DYNKF.

In other words the value of ZW1 is adjusted at every dynamic operationuntil an optimum value is reached.

FIGS. 1(a) to (e) illustrate the method of the invention graphically.FIG. 1(a) shows the relationship between the values L and LF examined atstep 1 in FIG. 2. In the first two intervals ΔT shown in FIG. 1(a)L-LF>DYNERK is satisfied at the sampling time. In the third interval ΔTthe value L-LF<DYNERK. It will be appreciated that in actual practicedynamic engine operation would continue for several seconds. Thus ΔT maybe up to 10 seconds. FIG. 1(b) illustrates the value of thetimer/counter. At the clock pulse corresponding to the measuring pointon the graph for L the value in the timer/counter 13 is set to DYNANZand then runs down to zero. If L-LF>DYNERK is satisfied for severalsubsequent timing pulses the value in the timer/counter is held atDYNANZ until L-LF<DYNERK.

It will be noted that DYNANZ defines a time "window" during whichknocking is detected. The frequency of clock pulses and the length oftime DYNANZ must be chosen so as to ensure that knocking is efficientlydetected.

FIG. 1(c) shows the value of LAST ZW2 changing with time. The value LASTZW2 is decremented as the timer/counter is decremented. The length oftime taken for the ignition angle to return to the normal characteristicvalue ALFA-Z varies depending on the initial value of LAST ZW2 which isLAST ZW1. The time taken for the ignition angle to return to normal isindicated in FIG. 1(c) as AUFREG.

FIG. 1(d) illustrates the setting of the acceleration knock flag and thenormal knock flag. The solid line indicates the acceleration knock flagand the dotted line indicates the normal knock flag. In the firstinterval ΔT shown, acceleration knocking of intensity greater than DYNKFis detected and the acceleration knock flag is set at some time duringthe period DYNANZ. It is reset to zero at step 18 after the time DYNANZhas expired. In the second interval, the intensity of knockingdetermined during DYNANZ is greater than NORMKF but less than or equalto DYNKF so that the normal knock flag is set (step 10). The normalknock flag is reset at step 12 after DYNANZ has expired.

FIG. 1(e) shows the variation of ZW1 with time. Acceleration knocking isdetected during the first measuring interval Δ T as indicated by theflag in FIG. 1(d) and therefore after the time DYNANZ at which steps 11through 20 are carried out, the value of ZW1 is increased by ΔZW1.During the second measuring interval shown in FIG. 1 the normal knockflag is set and no further adjustment of ZW1 is required.

It is clear from the above description that the method of the inventionis adaptive for the ambient conditions occurring during each operationof the engine. Each time it is sensed that the engine is in dynamicoperation the value of ZW1 is altered until the engine is temporarilyretarded just enough to avoid knocking combustions of a selectableintensity. When starting the engine the adaptive value LAST ZW1 is setto a defined initial value.

An important point to note is that the selectable intensity mentionedabove, i.e. DYNKF can be changed so as to adapt the method for differentengines for example. Thus the method is versatile and can be used inmany applications.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmethods differing from the types described above.

While the invention has been illustrated and described as embodied in anadaptive acceleration knock control, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. A method of mitigating accelerationknocking in internal combustion engines comprising the steps of sensingacceleration of an internal combustion engine; detecting occurrence of aknocking during the acceleration; and adjusting an amount of change ofan engine operation parameter for a next acceleration depending onwhether or not the knocking during acceleration is occurring.
 2. Amethod as defined in claim 1, wherein said adjusting step includesadjusting an ignition timing which is retarded in response to thesensing of acceleration.
 3. The method as defined in claim 2, whereinsaid adjusting step includes increasing an amount of retardation when aknock intensity exceeds an upper predetermined value, and decreasing theamount of retardation when the knock intensity is below a lowerpredetermined value.
 4. A method as defined in claim 1, wherein saiddetecting step includes examining an intensity of the knocking duringacceleration, said adjusting step including adjusting the amount ofchange of said engine operation parameter in dependence on the detectedintensity of the knocking during acceleration.
 5. A method as defined inclaim 4, wherein said examining step includes examining the intensity ofthe knocking during acceleration at regular intervals during apredetermined time after the sensing of acceleration.
 6. A method asdefined in claim 4, wherein said adjusting step includes adjusting theamount of change of the engine operation parameter when the intensity ofthe knocking during acceleration is outside a predetermined range.
 7. Amethod as defined in claim 6, wherein the predetermined range has alower limit selected such that only the knocking which does not requirecorrective action has an intensity below the lower limit.
 8. A method asdefined in claim 6, wherein the predetermined range has an upper limitselected such that only knocking caused by the effects of theacceleration has an intensity exceeding said upper limit.